1. Field
The present application relates to voice telephony, and more particularly to transport of control and status information for third party call control over packet switched networks.
2. Related Art
Voice telephony remains a major application of interest for business and personal use. In an example corporate setting, a telephony installation at a site can have a large number of users connected to a Private Branch Exchange (PBX) server, which can interface those users to a smaller number of outside lines (e.g., an E1 or T1 line) (a PBX can be implemented using a server with telephony cards for example, and more generally, functions that are often attributable to a PBX can be distributed to different entities in a connected system, and the term PBX is used for convenience herein, rather than by way of limitation). Such a corporation can have multiple sites with multiple PBX servers. The PBX at each site can provide a variety of services to users, such as call forwarding, park, conferencing, and so on.
It is increasingly desirable to extend these kinds of PBX services (or other services that may be available from a PBX) to mobile devices. For example, a service that allows a PBX to dial out on behalf of a mobile device, and bridge a call at the PBX is helpful for mobile users. Providing control and status information from the PBX (or from other control points) to the devices involved in such a call continues to be an area open for further improvements.